Telephone transmission



Jan. 17, 1928. 1,656,609

G. SEIBT TELEPHONE TRANSMI S S ION I Filed Feb. 9. 1921 In; A TTO'RNEYPatented Jan. 17, 1928.

GEORG SEIBT, OF BERLIN-SCHONEBERG, GERMANY.

TELEPHONE TRANSMISSION.

Application filed February 9, 1921, Serial No. 443,695, and in GermanyJanuary 23, 1920.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. I..,1313.)

loudness of receivers by making the pole pieces of alloyed iron, byusing laminated iron instead of solid iron or by other means which tendto increase the permeation of the pole pieces, as for example theadoption of a magnetic by-pass at the point where the pole pieces arejoined to the permanent magnet (see German Patent 301,311).

But the advantages derived from these measures were not sufficientlymarked to give rise to the general adoption of the improved type oftelephone receiver.

The object of the present invention is to turn to account a specificproperty of the improved type of receiver which is that ata giveninductance of the receiver the energy consuming resistance of its coilsis considerably lower than in the case of the ordinary receivers invogue. The expression energy consuming resistance as used herein meansthe total losses in the system or circuit or any part thereof. In otherwords, this resistance is not equal to but greater than the resistancefor continuous current. For the purposes of illustration a few numericalvalues will be adduced.

A standard receiver with pole pieces of flat solid iron with three slotsto reduce eddy currents, and with coils whose resistance to continuouscurrent is Wg=60 ohms, has a self-induction of L=0.035 henries.

With alternating current of a frequency of 900 alternations theenergy-consuming resistance is Ww=l33 ohms.

An improved receiver with pole pieces of iron laminae of a thickness of0.3 ms. and a magnetic by-pass, and a self-induction of L=0.0l henrieshas a resistance to direct current of Wg=27 ohms and an energyconsumingresistance to alternating current amounting to Ww=59 ohms.

This shows that with the same current strength an improved, receiverwill not only produce a louder sound, but will also consume less energythan an ordinary standard .from which energy is measurement 0 receiver.Such improved receivers maybe termed low loss receivers. In the aboveexample the ratio of the energies consumed in the two receivers is as133 I is to 59 I Where I denotes the. current strength.

In the central battery telephone system the receivers are connected toinduction coils or transformers as shown in the drawing in which Fig. 1is a diagrammatic representation of the circuits when two lines areconnected for conversation.

Fig. 2 is a longitudinal section and Fig. 3 is an end view of atransformer or an induction coil used for carrying the invention intoeffect.

B is the central batteryat the exchange, D a choke coil, ac, b' .d ae,bf the two subscribers" lines, mitters, and T T are the transformerstaken by the receivers at the substations.

In large towns the resistance of a line of average length connecting asubscriber to his exchange is about 300 ohms. This is also theapproximate value of the transmitter resistance. A standard inductioncoil or transformer of the type now generally employed in connectionwith a receiver represents an apparatus with a self-induction of about0.047 henries and an energyconsuming resistance to alternating currentof 120 ohms. These values are obtained while the receiver is connectedto the transformer by connecting the terminals of the primary coil b abridge and making a self induction and resistance.

When the receiver is disconnected, i. e. when the secondary coil of thetransformer T carries no load, the self-induction L of its primary coilS is 0.11 henries, its resistance Wg to continuous current 16 ohms andthe energy-consuming alternating current resistance IVw=30 ohms.

The secondary coil S itself when dis-' connected from the receiver has aself-induction of L=0.064 henries at a continuous current resistance of9 26 and an alternating current resistance of IVw=35 ohms.

Now if an improved receiver, whose electrical data is given above, isconnected to the same transformer the values measured at the terminalsof the primary coil will be M and M the transin the line re resented bL=0.04=5 henries and an energy-consuming resistance VVw=60 ohms, or inother words the same transformer that, when connected to the old type ofreceiver, represented an energy-consuming resistance in the line of 120ohms only represents 60 ohms when the new receiver is connected to it.

This resistance of 60 ohms is small in comparison with the resistance ofthe other parts of the line circuit. Hence the former resistance couldbe considerably increased without noticeably affecting the strength ofthe talking current.

Now the specific object of the invention is to alter the properties ofthe transformer in such a manner that it will cause a stronger currentto 'be supplied to a receiver of the improved type.

This can be accomplished by increasing the self-induction of the primarycoil 8,. This will be demonstrated by the following short calculation:

Let L be the self-induction of the primary coil S L the self inductionof the secondary coil S M the coetlicient of mutual induction of the twocoils and L the self-induction of the receiver.

The E. M. F. produced in the coil S is (OM11, I being the currentstrength in the line or primary coil S In calculating the current I inthe secondary' coil S or in the receiver the ohmicresistances i. e., thepure ohmic resistance for continuous currents, and the other energyconsuming resistances (losses due to eddy currents and hysterisis) maybe disregarded as negligible. All resistances except those due toinductance are disregarded in the formula. Hence the current in thereceiver is I (OM11 The coeflicient M in transformers'in which themagnetic dispersion is smallas in the case of ordinary transformers ispractically It follows that I increases linearly with L Hence if atransformer with a'primary coil of greater self-induction is inserted inthe talking circuit the current I will actually be increased. At thesame time an increase of the energy-consuming resistance the combinationof the trans ormer an the receiver is obtained. .This increase of theenergy consuming resistance in the line is due to the increased selfinduction of the coils. The

. secondary coil secondary coil'has a back working effect to the primarycoil which is effective in the line as increased resistance when theinduction of the primary coil is increased.

The object aimed at thus appears to be attainable in a most simplemanner. But a very undesirable secondary effect is also obtained andthis is that the inductance which the transformer inserts in the linewhen sup- 240 ohms. This impedance is connected in series with atransmitter resistance of about 300 ohms and an average line resistancealso amounting to about 300 ohms. Hence this impedance does not greatlyalfect V the strength of the current in the line, particularly as it isonly to be added as a vectorial magnitude. But the state of things willbe entirely changed if the self-induction of the primary coil S isincreased more and more without any counter-acting measures beingadopted. The impedance of .the transformer when supplying current from"its secondary coil may then considerabl exceed'the ohmic resistance ofthe transmitter and the sub-' scribers line which would result in aconsiderable weakening of the talking current.

The prevention of this undesirable effect is a matter of primaryimportance. The

- method of accomplishing this in accordance with the invention consistsin simultaneously increasing the self-induction of the secondary coil Sof the transformer.

The result obtained by doing this will become apparent'from thefollowing calculation:

Let E be the voltage at the terminals of the primary coil S call theself-induction of this coil L let the self-induction of the S be L. thecoeilicient of mutual induction M, and let L be the selfinduction of thereceiver. Then, if the energy-consuming resistances be left out ofaccount and symbolical expressions be adopted, the following equationswill be applicable: e

E twL L Y O L191; i Hence since It follows that a transformer supplyingcurrent to a receiver will represent an impedance m the l1ne with aself-induction of From this formula it will be evident that thisinductance may be decreased in any desired measure by increasing L,. IfL is very large in comparison with L i. e. if the self-induction of thereceiver as compared with the self-induction of the secondary coil ofthe transformer may-be left out of account, the impedance in the linewould approximate zero.

The ideas underlying the invention may be briefly recapitulated asfollows:

Receivers with an improved magnetic circuit do not only produce loudersounds but also have a smaller energy-consuming resist- If a receiver ofthis kind is connected to the ordinary type of induction coil ortransformer of a subscribers instrument the energy-consuming resistanceof the transformer supplying current to the receiver will still besmall. This resistance-could be increased without appreciably weakeningthe talking current. By suitably proportioning the windings of thetransformer stronger currents are obtained in the receiver withoutincreasing the resistance in the line to such an extent as to bedetrimental. Increasing the self induction of both coils increases theresistance in the line, but not to such anextent as to be detrin'iental,that is, without appreciably weakening the talkin current. The changesmade in the transformer consist in increasing the self-induction of itstwo coils. An increase of the self-induction of the primary coil alonewould be sufiicient if it were not for the fact that the impedance ofthe transformer would become too great and thus weaken the talkingcurrents. To obviate this the self-induction of the secondary coil isalso increased.

Values that may be adopted for the selfinduction of practical inductioncoils or transformers are L =0.2 i henries for the primary coil and L==0.1 henries for the secondary coil. These values, however, may bevaried. The values, for instance, may be increased to twice or threetimes those mentioned, but as such values are increased more wire isrequired without increasing the output sufficiently to warrant theadditional cost. The values may also be less than those stated; forinstance, L,=0.18 and L =0.08. In this case, while the effect is good,it is not as good as for the values first mentioned, These values ofself induction, characterizing my improved transformer, are taken whenthe transformer is not under load, that is. when the receiver isdisconnected, and .When the term self induction is used in the claims itis to be understood to mean a self induction whose value is'determinedwhen the receiver is disconnected, or when not under load.

When animproved receiver with a selfinduction of L =0.04, a resistanceto con tinuous current of Wg=27 and an energy consuming resistance ofWw=59 is connected to a transformer of this kind the values measured atthe terminals of the transformer are: L=0.05 and VVw=100. The valuesL=0.05 and Ww=l00 are measured at the terminals of the primarytransformer coil while the receiver is connected to the secondary coil.

By practical tests it will be found that the loudness of the soundemitted by an improved receiver that is first connected to an ordinaryor standard induction coil and then to a transformer of the novel typewill be increased in the latter case by about In order to obtain thegreater self-induction required of the novel type-of transformer thepresent form with its open magnetic circuit is preferably departed fromand a design of the kind shown in Figs. 2 and 3 adopted.

As shown in Fig. 2 the magnetic circuit of this transformer iscompletely closed. It consists of thin iron punchings about 0.15 of amillimetre in thickness. On account of the small magnetic reluctance thequantity of copper needed in the windings is smaller than that requiredin the ordinary type of induction coil, even though its self inductionis greater. The measurements indicated in Figs. 2 and 3 are inmillimetres and if these are adopted and the primary coil is made of M00turns and the secondary coil of 940 turns, the values of theself-induction will be those hereinbefore stated, viz. L=024 and L,=0.1henries. The thickness of the wire is 0.21 millimetres.

It may be mentioned here that the magnitude of the self-induction of thereceiver may be selected arbitrarily. To obtain the effect that it isthe object of the invention to accomplish the self-induction of thetransformer must be adapted to that of the receiver in such a way thatthe quotient of the two self-inductions exceeds If the self-induction ofthe receiver were made twice as great, i. e. 0.08, the self-induction ofthc secondary coil ofthe transformer would also have to be doubled.

I claim:

l. The herein described method of eflitransformer, which consists inincreasing the "tions is greater than self-induction of the primary coilof said transformer so as to supply proportionately increased amounts ofenergy through said transformer to said receiver Without appreciablydecreasing the strength of the current in the line.

3. The herein described method of efliciently utilizing low lossreceivers in a telephone system having such a receiver and atransformer, which consists in making the self-induction of the primarycoil of the transformer of a value greater than 0.11 henries so as tosupply increased amounts of sound producing energy to said receiverthrough said transformer, and in giving such values of self-induction tothe secondary coil of the transformer and t0 the receiver that thequotient of their respective self-induc- %f, so as to maintain thestrength of the current in the line practically unchanged.

4; The herein described method of eificiently utilizing low lossreceivers in a telephone system having such a receiver and atransformer, WhlCh consists in lncreasmg the 5. The combination in atelephone system of a telephone receiver having a given selfinduction,and a transformer for transfer ring energy to said receiver andcomprising a primary coil having a self-induction greater than 0.11henries whereby more energy is transferred than through a primary coilof .11 henries, and a secondary coil having a self-induction greaterthan 0.064 henries and at least 1.6 times greater than theself-induction of said receiver, whereby the strength of the current inthe line is nevertheless maintained unchanged.

6. The combination in' a telephone system of a telephone receiver havinga given selfinduction and a minimum resistance, and a transformer fortransferring energy to said receiver and comprising a primary coilhaving a self-induction of approximately 0.24 henries whereby moreenergy is transferred than through a primary coil of .11 henries, and asecondary coil having a self-induction greater than 0.064 henries andapproximate- 1y 2.5 times greater than the self-induction of saidreceiver, whereby the strength of the current-in the line isnevertheless maintained unchanged. I

In testimony whereof I have signed this Y specification.

GEORG SEIBT.

